FIXME **This page is not fully translated, yet. Please help completing the translation.**\\ // (remove this paragraph once the translation is finished) // ==== IEEE 2020-2024 Standard Flare Test ==== ** I. Definition of Flare ** Flare refers to non-imaging light that propagates to the image plane along unintended optical paths, resulting in reduced image contrast and undesirable imaging artifacts. In this standard, "Flare" and "Stray light" are synonymous and used interchangeably. | {{yanding:成像质量评价:标准化测试:5.png?550|}} | | Figure 1: Optical path of flare imaging | As shown in the figure, imaging light (solid blue lines) undergoes unintended reflections inside the lens, generating non-imaging light (dashed blue lines). Such non-imaging light that does not follow the intended optical path is collectively referred to as flare. When this non-imaging light reaches the image plane, it interferes with normal imaging (e.g., reducing dynamic range, creating circular light spots, etc.). | {{yanding:成像质量评价:标准化测试:2.png?600|}} | | Figure 2: Common flare phenomena in daily life (Image source: WIKI) | ** II. Sources of Flare ** Sources of flare include, but are not limited to: ● Internal reflections between lens elements in the system ● Scattering caused by contamination (e.g., dust, fingerprints, oil smudges) ● Poor lens coatings ● Scattering and/or diffraction caused by bubbles within lens elements ● Optical adhesives ● Reflections from the inner barrel and other internal surfaces ● Cover glass of the image sensor ● Bond wires of the sensor ● External factors: such as windshields ● Inappropriate spectral cut-off filters ● Diffraction at the lens hood or aperture ● Reflection and scattering from the image sensor surface ● Deviations from the nominal design due to manufacturing tolerances ** III. Flare Test Methods ** The flare test defined in this standard includes two test methods: **Flare A** and **Flare B**: ** (1) Flare A Test: ** Based on the standard dot pattern from ISO 18844:2017, additional test points are added along the horizontal and vertical axes to cover a larger field of view and capture stray light in specific directions. The severity of stray light is quantitatively evaluated by calculating the stray light index F value. | {{yanding:成像质量评价:标准化测试:3.png?600|}} | | Figure 3: IEEE 2020-2024 Standard Flare A test chart | The formula for calculating the stray light index F is: $$F=\frac{S_{Black}}{S_{White}}\times 100\%$$ where $S_{Black}$ represents the average luminance of the black region; $S_{White}$ represents the average luminance of the four white regions surrounding the black region. | {{yanding:成像质量评价:标准化测试:4.png?300|}} | ^ Figure 4: ROI regions for F value calculation ^ In the visible light range, the variation in white luminance should be less than 5% (or radiance if the device under test detects infrared light). The reflectance of the black regions under visible light should be < 0.03% (this requirement should also be met under infrared light if the device under test detects infrared light). The optical density of the black dots in the transmissive chart should be at least OD 4.0. The distance between the device under test (DUT) and the test chart should be set so that the dot array matches the field of view, and it should not be less than the minimum focus distance of the DUT. The test should be conducted under controlled lighting conditions in a darkroom. The lighting requirements are as follows: 1. The front- or back-illuminated (recommended) target should be uniformly illuminated, with an illuminance variation of < 5% across the dots or light trap array. 2. There should be no direct reflections on the test target. 3. Light leakage around the back-illuminated chart is strictly prohibited. ** (2) Flare B Test: ** By rotating the point light source or the device under test (DUT), a strong light source is simulated incident on the lens from multiple angles such as horizontal, vertical, and diagonal. After capturing a series of images, the flare intensity/attenuation of the images is calculated, thereby deriving metrics such as average flare intensity/attenuation and worst flare intensity/attenuation to quantify the stray light performance of the camera. {{yanding:成像质量评价:标准化测试:6.png?400|}} The flare test setup can be configured in the following two ways:\\ 1. Fixed light source, rotating DUT: The collimated light source and light shield are fixed, and the angle of the DUT is changed via a rotation stage to perform the test. {{ :yanding:成像质量评价:标准化测试:2020_flareb.png?500 |}} 2. Rotating light source, fixed DUT: The position of the DUT is fixed, and the incident angle is changed by directly rotating the collimated light source. {{ :yanding:成像质量评价:标准化测试:2020_flareb2.png?500 |}} The calculation principles for the test metrics are as follows:\\ ** Single-Pixel Flare Image Illuminance **\\ Using a reference light source with a known luminance ($L_{ref}$) and its average grayscale response ($R_{ref}$) generated on the sensor, the actual flare grayscale value ($R_{flare}$) measured at each pixel (x, y) is converted into the true physical illuminance ($E_{flare}$).\\ $$E_{\text{flare } \theta, \phi}(x, y) = \pi L_{\text{ref}} \frac{T_{\text{ref}}}{T} \frac{R_{\text{flare,clipped}}(x,y)}{R_{\text{ref}}}$$ where: $E_{flare}$: single-pixel flare image illuminance; θ: azimuth angle of the light source; ϕ: field angle of the light source; x: image coordinate x; y: image coordinate y; T: exposure time, in seconds; $T_{ref}$: reference exposure time used to measure $R_{ref}$ and $L_{ref}$, in seconds; $L_{ref}$: luminance of the collimated light source; $R_{flare,clipped}$: linearized result of the per-pixel grayscale signal in the scene, with the minimum value clipped to 1; $R_{ref}$: average value of the linearized grayscale signal generated by the collimated light source.\\ To prevent calculation errors caused by noise, the lower limit of the grayscale signal $R_{flare}$ is first clipped to 1, i.e.,\\ $$R_{flare,clipped}(x,y)=max(R_{flare}(x,y),1)$$ where: $R_{flare,clipped}$ is the linearized per-pixel grayscale signal, with the minimum value clipped to 1; x is the image coordinate x; y is the image coordinate y; $R_{flare}$ is the linearized result of the per-pixel grayscale signal.\\ ** Single-Pixel Flare Intensity **\\ The physical illuminance of the flare is compared with the illuminance of the light source itself to obtain a relative value representing the flare attenuation at that pixel, expressed in decibels (dB). $$\text{Flare}_{dB,\theta,\phi}(x, y) = 20 \log_{10} \left( \frac{E_{\text{flare}\theta,\phi}(x, y)}{E_{\text{source}}} \right)$$ where $ \text{Flare}_{dB}$ is the flare intensity, in dB; $\theta$ is the azimuth angle of the light source; $\phi $ is the field angle of the light source; x is the image coordinate x.\\ ** Average Flare Intensity/Attenuation **\\ The arithmetic mean of the $FlareAverage_{dB \theta,\phi}$ values (i.e., the flare attenuation value of each pixel) for all pixels in the entire image is calculated. The formula is as follows:\\ $$FlareAverage_{dB \theta，\phi}=avg(Flare_{dB \theta，\phi}(x,y))$$ $FlareAverage_{dB }$ is the average flare intensity, in decibels (dB); $\theta$ is the azimuth angle of the light source; ${\phi}$ is the field angle of the light source; x is the image coordinate x; y is the image coordinate y; $Flare_{dB }$ is the flare attenuation, in decibels (dB).\\ ** Worst Flare Intensity/Attenuation **\\ The data with the maximum flare intensity in the image is taken. The calculation formula is:\\ $$FlareWorst_{dB \theta，\phi}=\max_{x,y}(Flare_{dB\theta,\phi}(x, y))$$ where: $FlareWorst_{dB}$ is the worst flare intensity/attenuation, in decibels (dB); $\theta$ is the azimuth angle of the light source; ${\phi}$ is the field angle of the light source; x is the image coordinate x; y is the image coordinate y; $Flare_{dB }$ is the flare attenuation, in decibels (dB).\\ ** IV. Yanding Equipment Support **\\ ** RT-Flare Camera Module Flare Comprehensive Tester ** \\ [[https://yanding.com/product/detail?id=1841|{{yanding:成像质量评价:标准化测试:rft.png?500|}}]] [[https://yanding.com/product/detail?id=1841|RFT-Flare Comprehensive Tester]] \\ The RFT-Flare Comprehensive Tester is a professional automated device independently developed by Yanding to quantify the flare level of camera modules. It supports not only wide-angle modules but also telephoto modules, meeting the testing requirements of various application scenarios. The lighting conditions and algorithms of this equipment strictly follow the IEEE 2020-2024 standard Flare B test method. The equipment uses a collimated light source system to accurately simulate a point light source at infinity. The algorithm comprehensively analyzes the image flare attenuation characteristics by combining parameters such as camera ISO sensitivity, exposure time, and shutter radius. The system automatically generates detailed flare attenuation reports, including attenuation heatmaps and average and worst attenuation curves, providing high-precision data for stray light evaluation of automotive cameras. {{yanding:成像质量评价:标准化测试:7.png?600|}} ** RIQA-ADAS Image Quality Analysis - ADAS Module **\\ RIQA-ADAS is a professional image quality analysis software specifically developed for autonomous driving and automotive cameras. Its Flare module algorithm is based on the IEEE 2020-2024 standard, capable of quantifying the flare level of camera modules and outputting metrics such as the stray light index F (%), average flare attenuation, and worst flare attenuation. Flare A Module: It can output the F (%) bar chart and the F value for each black dot. The smaller the F value, the less the impact of stray light on image quality. {{yanding:成像质量评价:标准化测试:flarea.png?600|}} Flare B Module: It can output line charts of flare data for a set of images under different lighting directions, along with specific average and worst flare values.\\ {{yanding:成像质量评价:标准化测试:fb-1.png?600|}} ** Light Source Required for Flare A Test Method: Transmissive Light Box **\\ {{ :yanding:成像质量评价:标准化测试:2020_flarea-2.png?400|}} [[https://yanding.com/product/detail?id=1821|LV-CCI-15F-IR]]\\ ** Test Chart Required for Flare A Test Method: Transmissive Flare Test Chart **\\ {{ :yanding:成像质量评价:标准化测试:2020_flarea-1.png?400|}} [[https://yanding.com/product/detail?id=1606|CP303-TI Transmissive Flare Test Chart]]